1. Field of the Invention
The present invention relates to an arteriosclerosis-degree evaluating apparatus for evaluating an arteriosclerosis degree of a living subject, based on pulse-wave-propagation-velocity-related information that is related to a velocity at which a pulse wave propagates through an artery of the subject; such as a pulse-wave propagation velocity itself, or a pulse-wave propagation time, and particularly relates to an arteriosclerosis-degree evaluating apparatus for evaluating an arteriosclerosis degree based on a change of pulse-wave-propagation-velocity-related information relative to a change of blood pressure.
2. Related Art Statement
The harder a blood vessel is, the faster a pulse wave propagates through the blood vessel. It is therefore known that arteriosclerosis can be diagnosed based on information related to a velocity at which a pulse wave propagates through an artery. It is also known that pulse-wave-propagation-velocity-related information is influenced by blood pressure. For example, it is known that the higher the blood pressure is, the higher the pulse wave propagation velocity is, that is, the lower the blood pressure is, the lower the pulse wave propagation velocity is. Thus, Japanese Patent Document No. 2001-190506 discloses an arteriosclerosis evaluating device which obtains pulse-wave-propagation-velocity-related information, measures blood pressure, and can diagnose an arteriosclerosis degree based on both the obtained information and the measured blood pressure.
However, recently, it has been elucidated that there are cases where though blood pressure changes, pulse-wave propagation velocity does not change so much and, in those very cases, arteriosclerosis has advanced and patents"" life expectancy is short. In those cases where pulse-wave propagation velocity does not change so much with blood pressure, it can be said that pulse-wave propagation velocity is so strongly influenced by arteriosclerosis. Thus, it can be said that even if pulse-wave propagation velocity is high and blood pressure is also high, arteriosclerosis has not advanced so much if the velocity lowers as the blood pressure lowers, and that it has advanced if the velocity does not lower so much as the blood pressure lowers.
However, conventionally, the cases where change of pulse-wave propagation velocity relative to change of blood pressure is known have been limited to few cases, e.g., cases where when antihypertensive drug is administered to patients, blood pressure and pulse-wave propagation velocity are measured before and after the administration so as to observe the therapeutic effect of the drug. Even in those cases, a long time is needed before the therapeutic effect appears. Thus, detecting change of pulse-wave propagation velocity relative to change of blood pressure needs a long time.
It is therefore an object of the present invention to provide an arteriosclerosis-degree evaluating apparatus which can quickly detect change of pulse-wave propagation velocity relative to change of blood pressure.
The above object has been achieved by the present invention. According to the present invention, there is provided an arteriosclerosis-degree evaluating apparatus, comprising a blood-pressure measuring device which iteratively measures a blood pressure value of a living subject; a pulse-wave-propagation-velocity-related-information obtaining device which iteratively obtains, at substantially a same time as a time when the blood-pressure measuring device measures each blood pressure value of the living subject, a piece of pulse-wave-propagation-velocity-related information that is related to a velocity at which a pulse wave propagates through an artery of the subject; and an output device which outputs a change of the pieces of pulse-wave-propagation-velocity-related information iteratively obtained by the pulse-wave-propagation-velocity-related-information obtaining device, relative to a change of the blood pressure values iteratively measured by the blood-pressure measuring device.
The arteriosclerosis-degree evaluating apparatus according to the present invention may be used with a patient whose blood pressure is increasing, e.g., because a physical load is being applied to the patient, or a patient whose blood pressure is decreasing, e.g., because the patient is resting after a physical load has been applied. The blood-pressure measuring device iteratively measures a blood pressure value of the patient, the pulse-wave-propagation-velocity-related-information obtaining device iteratively obtains, at substantially the same time as the time when the blood-pressure measuring device measures each blood pressure value of the patient, a piece of pulse-wave-propagation-velocity-related information, and the output device outputs a change of the pieces of pulse-wave-propagation-velocity-related information iteratively obtained, relative to a change of the blood pressure values iteratively measured. Thus, the present apparatus can quickly detect the change of the pieces of pulse-wave-propagation-velocity-related information, relative to the change of the blood pressure values.
Preferably, the blood-pressure measuring device comprises an inflatable cuff which is adapted to be worn on a portion of the subject; a blood-pressure-value determining means for determining the blood pressure value of the subject based on a signal obtained while a pressure in the cuff is changed; a pressure-pulse-wave detecting device which includes a pressure-pulse-wave sensor that is adapted to be pressed against a prescribed artery of the subject, and which continuously detects, through the pressure-pulse-wave sensor, a pressure pulse wave produced from the prescribed artery; a relationship determining means for determining a relationship between magnitude of pressure pulse wave, and blood pressure, based on at least one blood pressure value measured by the blood-pressure-value determining means and at least one magnitude of the pressure pulse wave detected by the pressure-pulse-wave detecting device; and a blood-pressure monitoring means for iteratively determining, according to the determined relationship, a monitor blood pressure value of the subject, based on a magnitude of each of heartbeat-synchronous pulses of the pressure pulse wave continuously detected by the pressure-pulse-wave detecting device, wherein the pulse-wave-propagation-velocity-related-information obtaining device iteratively obtains a piece of pulse-wave-propagation-velocity-related information at substantially a same time as a time when the blood-pressure monitoring means determines each monitor blood pressure value of the living subject, and wherein the output device outputs a change of the pieces of pulse-wave-propagation-velocity-related information iteratively obtained by the pulse-wave-propagation-velocity-related-information obtaining device, relative to a change of the monitor blood pressure values iteratively determined by the blood-pressure monitoring device.
When the present arteriosclerosis-degree evaluating apparatus is used with a patient whose blood pressure is increasing, or a patient whose blood pressure is decreasing, the blood-pressure monitoring means iteratively determines a monitor blood pressure value of the patient, the pulse-wave-propagation-velocity-related-information obtaining device iteratively obtains a piece of pulse-wave-propagation-velocity-related information at substantially a same time as a time when the blood-pressure monitoring means determines each monitor blood pressure value of the patient, and the output device outputs a change of the pieces of pulse-wave-propagation-velocity-related information iteratively obtained relative to a change of the monitor blood pressure values iteratively determined. Thus, the present apparatus can detect, in more detail, the change of the pieces of pulse-wave-propagation-velocity-related information relative to the change of the monitor blood pressure values, as compared with the case where blood pressure values are iteratively measured using a cuff.
Preferably, the output device displays, in a two-dimensional graph defined by an axis indicative of blood pressure and an axis of pulse-wave propagation velocity, a symbol at a position corresponding to each of the blood pressure values iteratively measured by the blood-pressure measuring device and a corresponding one of the pieces of pulse-wave-propagation-velocity-related information iteratively obtained by the pulse-wave-propagation-velocity-related-information obtaining device.
According to this feature, a medical person such as a doctor or a nurse can visually and easily recognize a change of pulse-wave-propagation-velocity-related information relative to a change of blood pressure, in each of a plurality of time periods; such as a change of pulse-wave-propagation-velocity-related information relative to an initial change of blood pressure, an overall tendency of change of pulse-wave-propagation-velocity-related information relative to change of blood pressure, or a change of pulse-wave-propagation-velocity-related information relative to a terminal change of blood pressure.
Preferably, the pulse-wave-propagation-velocity-related-information obtaining device iteratively obtains the piece of pulse-wave-propagation-velocity-related information that is related to the velocity at which the pulse wave propagates through the artery including an aorta of the subject.
According to this feature, the output device outputs a change of the pieces of pulse-wave-propagation-velocity-related information related to the artery including the aorta, relative to a change of the blood pressure values iteratively measured. The pulse-wave-propagation-velocity-related information related to the artery including the aorta provides an excellent predictive indicator about cardiovascular diseases. Thus, based on the change of pulse-wave-propagation-velocity-related information related to the artery including the aorta, relative to the change of blood pressure values, a medical person can make an accurate diagnosis about the risk of cardiovascular disease.
It is another object of the present invention to provide an arteriosclerosis-degree diagnosing method comprising the step of iteratively obtaining a piece of pulse-wave-propagation-velocity-related information from a patient whose blood pressure is increasing because a prescribed physical load is being applied to the patient, or a patient whose blood pressure is decreasing because the patient is resting after a prescribed physical load has been applied, and the step of diagnosing an arteriosclerosis degree of the patient based on a change of the pieces of pulse-wave-propagation-velocity-related information iteratively obtained.
According to this method, the blood pressure of the patient is changed by applying the physical load to the patient, and the pieces of pulse-wave-propagation-velocity-related information are iteratively obtained from the patient whose blood pressure is increasing because of the physical load, or the patient whose blood pressure is decreasing after the physical load. Thus, a change of the pieces of pulse-wave-propagation-velocity-related information relative to a change of blood pressure can be quickly detected.